I have committed a program that compiles a diff for the coverage of boundaries in the boundary tiles.
Start it with: java -cp mkgmap.jar uk.me.parabola.mkgmap.reader.osm.boundary.BoundaryDiff<boundsdir1> <boundsdir2>
The diff is created as a set of gpx files that shows removed areas (contained in boundsdir1 but not boundsdir2) and new areas (contained in boundsdir2 but not boundsdir1).
You can also limit the check to special tag=value combinations: java -cp mkgmap.jar uk.me.parabola.mkgmap.reader.osm.boundary.BoundaryDiff<boundsdir1> <boundsdir2> admin_level=2 admin_level=6
I know that this is a bit off topic for mkgmap but it is an easy spin-off product and I think it might explain questions like: "my street is not assigned a city using the new boundaries download. why?".
WanMil
For those who want to test it: I have reuploded the precompiled boundaries from 29.04. using the new boundary file format which is required to run the diff. http://www.navmaps.eu/wanmil/europe_bounds_20110429.zip WanMil